Hello Danny Cocks,
Thank you for the confirmation.
I'm pleased to hear that the issue has resolved itself after some time, and you are now able to delete the resource group without needing any additional permissions.
Since the issue has been resolved, I will document the problem along with the solution. Additionally, you are invited to participate in a survey regarding the posted issue. Your feedback can be beneficial to other community members who might encounter the same problem.
Issue: Unable to delete an existing managed application
Cause: Due to ingestion problems with the managed application deployments, its failed to delete and it was reported that the "resource group doesn't exist" immediately after its creation.
Resolution: The issue resolved itself after some time, and you can now delete the resource group as expected.
As per Microsoft's recommendation, please consider Accepting the answer and upvoting it if the information provided was indeed. This can greatly benefit other community members.
You can refer to this document for more details: https://learn.microsoft.com/en-us/answers/support/accept-answer
Your support in this matter would be greatly appreciated and helpful to others.
Thanks